Answer:
A. The global mean temperature has gone up while the global pirate population has gone down.
Step-by-step explanation:
These two variables, the global mean temperature and the global pirate population, do not cause a change in the other. A decrease in the number of pirates, while it may coincide with an increase in the global temperature, is not caused by the change in temperature.
Similarly, an increase in the global temperature, while it may coincide with a decrease in the number of pirates, is not caused by having fewer pirates.